Cutaneous Fistula Caused by Metallosis Following Rigid Spinal Fixation: A Rare but Important Diagnostic Consideration.

Metallosis is a rare complication of spinal instrumentation, typically associated with joint arthroplasty or fusionless constructs. Fistula formation due to metallosis is exceptionally uncommon, particularly in cases involving rigid spinal fixation. We report a case of a 48-year-old female patient who developed a cutaneous fistula at the site of a previous thoracic spinal fixation performed for a metastatic spinal tumor. Clinical examination revealed a small granulomatous mass with a fistula. Although dynamic radiographs showed no apparent instability, computed tomography revealed radiolucent halos around the screws in the right T4 and left T3 pedicles, indicating screw loosening. Magnetic resonance imaging demonstrated a sinus tract extending from the skin to the right T3 pedicle screw. Surgical excision of the fistula and hardware revision were performed. Histological analysis confirmed the presence of metal wear debris and a chronic inflammatory response consistent with metallosis. Bacterial cultures were negative. Despite the absence of typical intraoperative signs such as tissue discoloration or necrosis, metallosis was diagnosed pathologically. This case highlights the importance of considering metallosis in the differential diagnosis of unexplained cutaneous lesions overlying spinal instrumentation. Even in the absence of instability or typical intraoperative findings, metallosis may present solely with skin manifestations such as fistula formation. Early recognition is essential for appropriate management.